The overall goal of our research project is to understand how virus-encoded information determines infectivity, host range and other interactions of mRNA viruses with their hosts. We are particularly interested in the molecular mechanisms by which recombination processes between genomic RNAs provide these viruses with some special means for their flexibility and rapid evolution. In this project we will contribute to the understanding of recombination processes in multipartite mRNA viruses. We will study three closely related model bromoviruses: brome mosaic virus, cowpea chlorotic mottle virus and broad bean mottle virus. By using various bromoviral RNA mutants, we will investigate recombination in whole plants and in plant protoplasts. Homologous recombination between various bromoviral RNA components will be studied using infectious mutations in both coding and noncoding regions. To investigate sequence and structural factors which determine recombination, the sites of recombination will be localized over bromoviral RNA genome and sequences around these sites will be characterized. Experiments will be undertaken to elucidate at what stage of RNA synthesis the recombination occurs. The primary importance of this work lies in its impact on fundamental virology and biology; the results are directly applicable for other RNA viruses infecting both animals and plants.